Structures formed of concrete and other masonry or cementitious materials often require reinforcement in their construction. These concrete materials have low tensile strength yet have good compressive strength. When using concrete as a structural member, for example, in a bridge, building or the like, reinforcement is often used to impart the necessary tensile strength. In new and existing concrete structures, such as precast driveways, slabs, sidewalks, pipe etc., reinforcement has been undertaken with a variety of steel shapes such as open steel meshes, steel rebar, and steel grids. Steel grids have been used in reinforcing concrete structures such as decking for drawbridges. These steel grids are a closed cell structure, and each section of steel grid contains and confines a rectangular or square column of concrete. These types of grids are inherently very inefficient in their use of the reinforcing material.
Steel and other metals used as a reinforcing agent are subject to corrosion. The products of corrosion result in an expansion of the column of the steel which causes a "spalling" effect which can cause a breakup and deterioration of the concrete structure. This breaking and crumbling of concrete structures is severe in areas of high humidity and areas where salt is used frequently on roads, driveways and sidewalks to melt ice or snow. Bridges over waterways in areas such as the Florida coast or Florida Keys are exposed to ocean air which causes deterioration and a short lifespan requiring constant rebuilding of these bridges. Concrete structures in the Middle East use concrete made with the local acidic sand which also causes corrosion of steel reinforcements.
In addition, because of the potential for spalling due to corroded metal reinforcing members, such configurations typically require a minimum of one inch or more of "cover" meaning that the steel reinforcing members are spaced at least about one inch from the surface of the concrete. This requires that the design thickness of concrete members, such as panels, must be of a certain minimum thickness, usually about three inches, to allow for the thickness of the steel reinforcing member and about one inch of concrete on either side of the reinforcing member. This minimum thickness to avoid spalling causes certain design constraints and requires a relatively high weight per square foot of surface area of the panel.
To replace traditional steel in reinforcing concrete, many types of plastics have been considered. One attempted replacement for steel in reinforcement uses steel rebars coated with epoxy resin. Complete coating coverage of the steel with epoxy, however, is difficult. Also, due to the harsh handling conditions in the field, the surface of the epoxy coated steel rebars frequently will be nicked. This nicking results in the promotion of localized, aggressive corrosion of the steel and results in the same problems as described above.
Fiberglass composite rebars have been used in reinforcing concrete structures such as the walls and floors of x-ray rooms in hospitals where metallic forms of reinforcement are not permitted. The method of use is similar to steel rebars. The fiberglass composite rebars have longitudinal discrete forms which are configured into matrixes using manual labor. Concrete is then poured onto this matrix structure arrangement.
Fiberglass composite rebars are similar to steel rebars in that the surface is deformed. Fiberglass gratings which are similar to steel walkway gratings also have been used as reinforcements in concrete, but their construction, which forms solid walls, does not allow the free movement of matrix material. This is due to the fact that the "Z" axis or vertical axis reinforcements form solid walls.
In dealing with reinforcing concrete support columns or structures, wraps have been applied around the columns to act like girdles and prevent the concrete from expanding and crumbling. Concrete is not a ductile material, thus, this type of reinforcing is for only the external portion of the column. One type of wrap consists of wrapping a fabric impregnated with a liquid thermosetting resin around the columns. The typical construction of these wraps has glass fiber in the hoop direction of the column and glass and Kevlar fibers in the column length direction. Another approach uses carbon fiber unidirectional (hoop direction) impregnated strips or strands which are designed to be wound under tension around deteriorated columns. The resulting composite is cured in place using an external heat source. In these approaches the materials used in the reinforcing wraps are essentially applied to the concrete column in an uncured state, although a prepreg substrate may be employed which is in a "semi-cured" state, i.e. cured to the B-stage. When using a woven fabric, "kinking" can take place when using either carbon or glass fibers, because the weaving process induces inherent "kinks" in either a woven wet laminate or woven prepreg, which results in a less than perfectly straight fiber being wrapped around the column.
Another approach to reinforcing concrete structures and columns is to weld steel plates around the concrete columns to give support to the concrete wall. Such steel plates are also subject to corrosion and loosening resulting from deterioration of the column being supported. This approach is only an external reinforcement and lacks an acceptable aesthetic appearance which makes it undesirable.
An approach to reinforcing concrete mixes has been using short (1/4 to 1") steel, nylon or polypropylene fibers. Bare "E-type" glass fibers are generally not used due to the susceptibility of glass fibers to alkaline attack in Portland cement.
An exemplary structural reinforcing member for asphalt and concrete roadways and other structures is provided in U.S. Pat. No. 5,836,715, which is incorporated herein by reference. The reinforcing member disclosed therein comprises a gridwork having a set of warp strands and a set of weft strands disposed at substantially right angles to each other. The gridwork is impregnated substantially throughout with a resin so as to interlock the strands at their crossover points. The set of warp strands is separated into groups each containing a plurality of contiguous strands, with at least one strand of each group lying on one side of the set of weft strands, and at least one other strand of each group lying on the other side of the set of weft strands in contiguous superimposed relationship with the other strand of the group on the other side of the weft strands. The strands may be composed of glass (suitably E-type glass), carbon, aramid, or nylon. As noted above, however, the use of glass fibers in cementitious materials can be difficult because of the susceptibility of glass fibers to alkaline attack in Portland cement. In addition, others of the fibers disclosed by the patent have individual disadvantages such as the relatively high cost of carbon, notwithstanding its exceptional strength and resistance to alkaline attack in concrete.
Thus, there is a need for improved structural members adapted to reinforce a variety of products. For example, there continues to be a need for a structural reinforcement member for concrete structures which accomplishes the reinforcement or increases material properties of the concrete structure without being subject to corrosion or attack. Such a structural reinforcement member would preferably not only be resistant to corrosion or attack, but would also be relatively inexpensive. There also remains a need for methods to reinforce products using these structural members.
It is an object of the invention to overcome the deficiencies of the prior art as noted. A more particular object of this invention is to provide a structural member adapted to effectively reinforce a variety of different products, including relatively thin walled concrete panels. A further object of the invention is to provide methods for utilizing the structural member adapted to reinforce a product, and for efficiently producing the structural member.